In pressurized gas-insulated switchgear stations, the solid insulation components are disc-like in shape with some complex sub-structural features including central metallic inserts.
DE 33 11 218 A1 discloses a disc-type insulator for enclosed high-voltage equipment. The insulator includes a cast-in electrode which is segmented and which extends peripherally and concentrically with respect to the edge surface of the disc. The cast-in electrode is connected to contact electrodes by means of contact tongues; the contact electrodes bearing against a metal mounting ring. To avoid damage to the disc-type insulator, to the contact tongues, or to the cast-in electrode during shrinkage of the disc-type insulator, following its casting, or damage resulting from thermal stresses during operation, the cast-in electrode is divided into a plurality of electrode segments which follow one another in the peripheral direction.
DE 40 15 929 A1 discloses a solid insulator, which is intended for a gas-insulated metal-encapsulated high-voltage installation. It has an insulator body containing a cast resin, an electrode, which is supported by the insulator body and is provided for carrying high voltage, a retaining part which can be mounted on the metal encapsulation and a field control element, which is cast onto the insulator body and consists of electrically conductive plastic. The insulator is intended to reliably prevent mechanical damage to the insulator body and/or irreversible damage caused by long-term dielectric stresses.
Such disk-like insulation components consist of a vacuum-cast, mineral-filled (i.e. SiO2, Al2O3 or CaSiO3), anhydride-cured Bisphenol-A epoxy, sustaining the current mechanical and electrical loads. In gas insulated switchgear substations, solid insulation components are submitted to both high electrical field and high mechanical loads, such as hydrostatic pressures and bending moments.
The main drawbacks of mineral-particle-filled epoxy gas insulated switchgear insulators are the heavy weight of such components (e.g. two to three people are required to handle the biggest insulators, i.e. more than 30 kg), the limited mechanical performance and relative brittleness of the material, leading to catastrophic failure mechanisms.